Foiling wise when using a single in front of the tunnel I use a laminar flow foil, with the thickest part of the chord back at about 45% aft, like the top foiling the picture below, but for a tunnel on its own bring the thickest part of the fin forward to about 30% aft like the bottom picture. The reason for is that with a fin in front of the tunnel the angle of attack of the tunnel is controlled, so a lower drag laminar flow foil can be used, with the tunnel alone it needs the foil proportion more forward as that enables the fin to handle greater angles of attack. I also make a stand alone tunnel a tad thicker for the same reason.
great diagram. thanks. Ive been searching for a 10" pvc pipe and have been failing. the only place i found one wanted to sell me a minimum of 20 ft, i guess ppl don't deal in foot long sections for woodworking laminating purposes, so I'm going to call a few contractors in the area and see if they will have any scrap kicking around at the construction site. Roy your rampant video shows you making a tunnel with an internal layer of 6 oz glass correct? would a wooden layup with internal layers of glass cloth be acceptable in making a strong single tunnel capable of taking abuse ?
Roy I've seen on some of your boards what appear to be black or metallic fins that are curved.. like the predator I think its called, are those an example of paper layup fins? Those things look unreal and must perform nicely
The tunnel for the 'Rampant has two layers of 3mm wood with a glass layer in between. because the glass layer is on the neutral axis it doesn't add much strength, it's really there to give some structure to the thinned out trailing edge. Glassing on the outside is best done after foiling. Glassing the inside is tricky to do because the cloth can't be pulled tight, but it can be done.
The black/metallic fins are coated with epoxy resin mixed with graphite powder. this makes a very fast and abrasion resistant surface and the graphite powder is cheap, only $5 per half a litre or so, WEST system sell it I think. the graphite coated fins are marine ply ( some of them glassed with kevlar ) or glass/epoxy also there is a tri fin tunnel setup which is paulownia covered with resin, graphite and white pigment to make a metallic grey.
If you can't find plumbing pipe a mould can be made with two semi circular end pieces covered with thin ply bent around it.
A two layer wooden tunnel glassed both sides would be fine, easier to glass the inside if you don't foil the inside, but I'd go for a paper and resin layup, tinted or covered with graphite, it's up to you though. If doing a big wooden tunnel making it thicker will help with strength, also harder wood makes them stronger, though heavier. paper and resin is heavier than cedar of course but because it can be made thinner it winds up fairly light.
Always interesting to see another builders perspectives on a build, especially when well thought out. I'm getting some good ideas from this thread for the next one. I'm really interested in seeing this tunnel go together! Keep us posted with as many Pics as you care to take!
Now that all the hazing and the my d!ck is better than your d!ck banter is behind us, I've gotta say I'm enjoying y'alls discussion on how to build these boards. Very informative and interesting. Thanks
So I've decided to stick with wood to make the tunnel. I'm going to put a layer of glass inside and glass the entire outside with 6 oz glass when done. That should be pretty solid right. ?
It is important to me to keep the wood look. image.jpg